The present invention relates to an image forming apparatus, which has a fixing apparatus for fixing an image to a sheet.
Generally, in image forming of an electrophotographic system, a toner image is fixed by application of heat and pressure.
Since fixing temperature is usually high temperature of 200° C., an influence of heat generated by a fixing device poses a problem to each part in the image forming apparatus, and various countermeasures have been taken hitherto.
Unexamined Japanese Patent Application Publication No. 2005-77996 discloses a technology that the heat generated by a fixing device is intercepted by using a heat insulation material made from a porous ceramic to housing of the fixing device.
In Unexamined Japanese Patent Application Publication No. 2005-338430, it is proposed that a heat insulation body, which intercepts heat of the fixing device, is structured to be one layer or multiple layer structure.
In Unexamined Japanese Patent Application Publication No. 2004-109732, it is proposed that in order to cool a roller, which conveys a sheet ejected from a fixing device, cool air introduced from outside is put onto the roller.
In an image forming apparatus, which intercepts the heat of the fixing device using the heat insulation material, the heat insulation material is put to the heat for a long time when the fixing device is used for a long period of time. As a result, the heat insulation material deteriorates and its insulation efficiency declines. Also there is a problem that the parts inside the image forming apparatus are influenced by the heat generated by the fixing device.
In addition, although intercepting the heat from the fixing device by the heat insulation device of a sealed structure, in which the air is the heat insulation layer, is also considered, the temperature of the air configuring the heat insulation layer rises and the heat insulation effect declines by prolonged use.
Furthermore, in case when cooling the fixing device by introducing cool air from outside, the cool air spreads inside the fixing device and lowers the temperature of a heating roller, and in order to overcome the reduction in the temperature of the heating roller, electric power is consumed. As a result, a problem with a power dissipation increasing arises.